Magnetic recording media such as magnetic disks have been extensively used, and efforts have been made to increase bit density on such magnetic media. Today, the bit density on a magnetic disk, for example, often exceeds 1 G bits/in.sup.2. In order to further increase the bit density on a magnetic medium, it seems necessary to provide an improved magnetic write/read head. The most promising one is an induction type magnetic head.
A typical induction type magnetic head utilizes a coil wound on a block of magnetic core. In order to minimize the dimensions of the head, however, many of recent induction type magnetic heads incorporate a thin film.
As shown in FIG. 1, a magnetic head incorporating a thin film has a spiral induction coil 101, part of which is configured to pass through in between a lower core layer 102 and an upper core layer 103. Since the lower core layer 102 and the upper core layer 103 are made of conductive magnetic materials such as NiFe, the induction coil 101 is electrically insulated from the core layers 102 and 103 by an insulating layer 104. This type of induction type magnetic heads has a face that faces a magnetic disk such that the face has a write/read gap g between the lower core layer 102 and the upper core layer 103 for performing write and read operations, as shown in FIG. 1A.
The upper core layer 103 has on the face thereof a section which has an elongate pole 103a, as shown in FIG. 1B. The elongate pole 103 is configured such that the magnetic flux density H through it becomes greatest at the tip thereof.
A well known technique to form such elongate pole 103 is a photo-lithography in which the upper layer 103 is etched using a photo-resist mask.
In order to increase bit density in magnetic recording, it is necessary to make the width W of the elongate pole 103a small, as shown in FIGS. 1C and 1D, which may be attained by forming the tip of the elongate pole 103a in the form of thin rectangle having a narrow tip (called elongate pole-tip) 103b, as described in IEEE TRANSACTIONS ON MAGNETICS, Vol. 26, No. 5, September 1990 by James L. Su et al. According to this article, the maximum ratio of the width W2 of the elongate pole-tip 103b to the width W1 of the elongate pole 103a, W2/W1, is found to be 0.46, with W1 being 26 micrometers and W2 12 microns.
If a further increase in bit density is intended, the width W2 of the elongate pole-tip 103b must be further narrowed. However, it is difficult to form a elongate pole-tip having a width less than 2.5 microns in the photo-lithographic method, since the thickness of the upper core layer 103 is then of order of a few micron.
Furthermore, if the rectangular elongate pole-tip 103b is made about 2.5 micrometers wide, it is likely that the magnetic flux can saturate at the root section of the elongate pole 103b, and, should the magnetic flux saturate, change in magnetic field would not propagate beyond the saturated region, so that the tip of the elongate pole-tip 103b would become insensitive, thereby degrading over-write characteristic of the head.
Another related technology for providing a elongate pole configuration is described in U.S. Pat. No. 5,600,519. This patent discloses a thin film magnetic head having three sections defined by a flare point and a zero throat height. The width of the intermediate section between the flare point and the zero throat height progressively increases toward the flare point, as shown in FIGS. 12 and 13 of the aforementioned patent. This increase in the elongate pole dimension is to equalize the flux density in the elongate pole. However, this patent does not teach any influence of the head configuration on the over-write characteristic.
There is disclosed in Japanese Patent Publication Laid Open No. 2-105308 another form of the pole tip in which the elongate pole changes its width towards the pole tip at a given angle. This prior art also fails to teach any influence of the angle of the elongate pole on the over-write characteristic.
It is an object of the invention to provide a magnetic head which has an enhanced magnetic flux density in the pole tip, even when the width of the pole tip is 2.5 microns or less.